The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Active Fuel Management (AFM) improves fuel economy of a vehicle via deactivation of selected engine cylinders during operation of an internal combustion engine (ICE). For example, an eight-cylinder engine may have four cylinders deactivated during a highway cruising event when engine load and/or requested torque is less than a respective threshold(s). All of the engine's cylinders may be activated to provide a requested engine torque during a state of wide-open-throttle engine operation or during an uphill driving event.
Intake and exhaust valves of a cylinder may be prevented from opening, and maintained in a closed state during cylinder deactivation. An engine cylinder does not produce power when deactivated. Exhaust gas may be retained in the cylinder when the cylinder is deactivated. The retained exhaust gas is iteratively compressed and uncompressed during intake, compression, ignition and exhaust strokes of other active cylinders. The deactivated cylinders provide essentially zero net output torque to a crankshaft of an engine.
An engine cylinder generates torque when activated. The torque is provided to a crankshaft that drives a driveline of a vehicle. A positive torque is generated by the engine cylinder during vehicle acceleration and a negative torque is generated during engine braking. The negative torque may be used to decelerate the vehicle. Engine braking reduces brake-pad wear and prevents brake overheating during sustained braking, such as during a downhill braking event. Engine braking may be used in conjunction with sustained wheel braking during a downhill driving event to maintain a constant vehicle speed.
Minimal engine braking torque is provided by a deactivated cylinder. The more cylinders that are deactivated, the more overall engine braking torque is reduced.